The present invention relates generally to overhead cranes used in present-day industries, and more particularly to means for removing worn or broken wheel assemblies from such cranes and reinstalling spare wheel assemblies.
Industrial overhead cranes comprise an "end truck" having four or more wheels that ride on overhead parallel rails located near the ceilings of industrial plants and factories. End trucks support the ends of a bridge of an overhead crane that spans the distance between the parallel overhead rails. Such cranes and trucks are, of course, used to transport heavy objects that can be lifted and lowered by an electrical winch or winches that are an integral part of such cranes.
The wheels of most domestic crane trucks have double flanges, as depicted in FIG. 4 of the subject drawings, that maintain the wheels on the parallel rails, but some wheels have only one flange, and some have none. In addition, each wheel is an assembly of components that includes bearings, spindles, bearing races and housings (that house the bearings), shafts, flanges and other components. The wheels per se are forged steel structures that can be brittle such that the wheel flanges break or running surfaces become worn, which then requires replacement of the wheel assembly. In addition, bearings, bearing races and wheel spindles and shafts become worn, which, again, requires removal of the worn assembly and reinstallation of a spare wheel assembly.
The precision at which crane wheel components are required to operate may not be apparent, but it can be appreciated that the overhead rails upon which the crane travels must be as near perfectly parallel as possible. Otherwise, the wheels and wheel assemblies will not "track" the rails properly, and will be subject to lateral forces imposed upon wheel flanges and other wheel components while traveling on the rails. Precise alignment of the end truck, wheel assembly and crane wheels is critical due to the following: Wheel flanges that ride on the rails cause a high amount of friction resulting in: (1) wheel wear ($15,000 each), (2) rail wear, which are, of course, difficult to change, (3) increased motor loads on crane drive system, resulting in blown fuses and motor damage. This can result in inability to move the crane in a desired direction.
Heretofore, the industry accepted practice of removing worn or damaged crane wheel assemblies, with each assembly weighing as much as 2000 pounds or more, is unbolting the wheel assembly from the crane truck, manually rolling the wheel assembly unsupported out from under the end of the truck longitudinally along the rail beneath the truck and wheel, and then placing a "choker" cable around the wheel so that the wheel could be lowered to the floor by a separate, floor operated, mobile crane. Personnel handling, actually manhandling, such assemblies worked from catwalks provided at the level of the rails.
Such a procedure places the mechanics working on the overhead crane at substantial risk due to the heavy wheel assembly being unsupported for the period of time it is removed from the crane truck to the occasion the floor crane is connected to the choker cable. In the case of overhead cranes used in potrooms that electrolytically smelt aluminum metal, strong magnetic fields are present that pull and jerk the wheel assembly about, as the magnetic fields acting on the assembly and on other iron and steel structures in and of the building housing the potrooms repel and attract the assembly such that it can be wrenched free of the personnel handling the wheel and either fall to ground level or fall back upon the catwalk and on personnel working on the catwalk. The strong magnetic fields are caused by electrical current flowing in large buses supplying current to the electrolytic cells of the potline.